With an electrophotographic process, a desired image is formed on a transfer material as follows. First, light from a copy lamp is applied to an image on a document, and a photoreceptor is charged to a predetermined potential by an electrostatic charger. Subsequently, reflected light from the image on the document is irradiated on the photoreceptor to form an electrostatic latent image. After developing the electrostatic latent image into a visible toner image with developer in a development device, the toner image is transferred to a transfer material by a transfer charger.
When an extremely large number of copies of the image are produced through the above-mentioned process, the developer deteriorates and causes flying toner. The flying toner makes a wide range of components, such as an optical system having a mirror and a lens, image forming processing elements including various chargers and a development device, and paper feed and transport systems dirty. Such dirt deteriorates the development characteristic, and degrades the image quality.
In recent years, in order to solve the above-mentioned problem, Japanese Publication for Unexamined Patent Application No. 67074/1992 (Tokukaihei 4-67074) proposed a technique for detecting the dirt on.a charger 202 with an optical sensor 201 as shown in FIG. 42. Moreover, as illustrated in FIG. 43, Japanese Publication for Unexamined Patent Application No. 75479/1994 (Tokukaihei 6-75479) proposed a technique for detecting a fog on a photoreceptor 303 by optical sensors 301 and 302, adjusting the amount of light from the copy lamp or the developing bias, and controlling the agitation of developer.
However, the above conventional image forming apparatuses do not fully consider a structure for satisfactorily preventing flying toner that makes the inside of the apparatus dirty. Therefore, such apparatuses cannot sufficiently prevent the dirt inside the apparatuses caused by the flying toner.